Method and apparatus for coating dry rectifier elements



March I, 1949.

w. E. RIECKEN 1 2,462,899 METHOD AND APPARATUS FOR COATING DRY RECTIFIER ELEMENTS Filed March 20, 1944 INVENTOR. W/LL/AM f. lP/fC/ff/V Patented Mar. 1, 1949 METHOD AND APPARATUS FOR COATING DRY RECTIFIER ELEMENTS William E. Riecken, Leonia, N. J., assignor to Federal Telephone & Radio Corporation, New York, N. Y., a corporation of Delaware Application March 20, 1944, Serial No. 527,178

1 This invention relates to the manufacture of dry rectifier elements and particularly to a process for applying insulating coating to selected portions of the semi-conducting layer and subsequently coating said partially insulated layer with a metallic counter-electrode.

Dry rectifier elements generally comprise a metallic base plate, a semi-conducting layer such as a layer of selenium thereon, and a metallic counter-electrode coverin said layer. When a plurality of such elements are assembled in a stack and held together under pressure, the pressure may cause short circuits through the semi-conducting layers, which are very thin.

It therefore is desirable to provide a localized layer of insulating material between the semiconducting layer and the counter-electrode covering the area where pressure is exerted and leaving the remainder of the semi-conducting layer bare for direct contact with the counter-electrode. Moreover, the additional thickness provided by the insulation may be utilized to raise the registering portions of the counter-electrode above the level of the portions contacting the semi-conducting layer, which further serves to concentrate pressure on the insulated areas.

In certain instances, and particularly when the rectifier elements are small and have no central mounting hole, the insulating material in the form of a lacquer or paint may advantageously be applied on opposite segments of the -semi-conductin layer, as by applying a maskingstrip covering the central portion of the element and then coating the exposed segments. Thismay advantageously be carried out by simultaneously masking and coating a plurality of such elements mounted in a row and centrally covered by the samemask. However, it has been found somewhat difllcult to provide a sufliciently tight engagement between the mask and the element surfaces to prevent the liquid insulating material from creeping under the edges of the mask. This is especially true when the rectifier elements are partially punched from a strip of metal and are processed in that condition, since it is very difii- 8 Claims. (Cl. 29-1555) relative level of such elements. A further object is to provide a suitable support-for the elements during masking and coating, and in particular a support on which a plurality of elements carried by a mounting strip can readily be placed, masked, coated and removed under production conditions.

These objects are in general accomplished by mounting the rectifier elements on a flexible strip, which may be a metal strip from which they have been partially punched, and bending said strip so that the successive semi-conducting surfaces of the elements are arranged along a convex curve. By applying the masking tape lengthwise along such elements and pulling it tightly, the curvature of the unit will serve to maintain the necessary tight contact between the tape and each element, regardlessof slight variations in the elevations of the element surfaces above the sup-- porting strips, since the tape is deflected downwardly at opposite sides of each element.

In the preferred embodiment, a curved support for the mounting strip is employed, against which the strip is held during application of the insulation. A feature of the invention is the utilization of the masking tape to hold a flexible support in curved position, which is readily accomplished by detachably fastening the tape adjacent one end of the support, drawing the tape tightly down across the series of elements and detachably fastening it adjacent the other end of the strip. This method is especially advantageous since the masking tape and series of elements can be rapidly applied to and removed from a support.

The invention also includes the provision of a suitable mounting strip support construction; and a specific feature comprises mounting clips for attaching and detaching the masking strip. In the embodiment shown herein, the support is in the form of a hand jig, arranged so that the element mounting strip and the masking tape can be rapidly and accurately attached to the support with one hand, followed by application of the insulating liquid and removal of the masking tape and mounting strip with the other hand in a convenient, accurate and rapid manner suitable for commercial production.

Other objects and advantages will appear from the following description considered in connection with the accompanying drawing, in which Fig. 1 is a side elevation of the jig with a mounting strip and masking tape in position for applying the insulation, a preliminary position being indicated in dotted lines;

Fig. 2 is a plan view of Fig. 1, and

H is then removed by drawing the ends of tape 11 from beneath clips I6. The insulation may 7 be allowed to dry before or after removal of the tape, according to the drying rate of the liquid used, and the strip II is then ready for--the application of the counter-electrode.

The desired arrangement is "adapted for very rapid application and removal A jig (2 for mounting the strip H in position for masking and coating is provided with a handle l3 centrally attached to a support plate I4 longitudinally curved andprovided with suitable means for holding strip II in flexed position against its convex surface. In the illustrated construction a bifurcated hook I5 is formed integrally at one end of support 14, arranged to engage an end of the strip l l which may be slipped under the hook.

A tape clip attached to the bottom of the support l4 near one end extends inwardly and diverges from the support to provide a clamping notch into which the end of the masking tape l I maybe drawn and firmly held. In the form shown the clip 15 is provided with a sharp edge I8 across which the tape end may be drawn to sever it. A central tape-locating notch 19 extends through the end of support l4 and hook l5 and advantageously is just wide enough to receive the tape and hold it in registered central position. The opposite end of support 14 is provided with a similar clip l6 and notch 19. The inner end of around the edge 20.

Suitable side guides 2| for maintaining the mounting strip H in registered central position may be carried by support l4, and in the form illustrated consist of metal strips attached to the support plate l l by the same rivets 22 used to attach clips l6. Each guide 2i has upturned ends projecting above plate [4 and fitting the sides of strip ll, said ends being slightly flared outwardly to facilitate insertion of the strip; The guides 2| are advantageously located adjacent the ends of support plate I4.

The strip H, carrying elements 10 to which the semi-conducting layer has'already been applied, is placed with one end under the hook H5 in the position indicated in dottedlines in Fig. 1. An end of the masking tape l1 iswedged beneath the right hand clip I6 and cut ofi against the edge I8 if desired. It is then bent around edge 20, brought up through notch l9, thence across the elements ID, and is drawn downwardly through the opposite notch l9, pulling the strip I l against the curved face of support I4. The left hand end of the tape is then brought under the support but around edge and drawn between the plate l4 and the left hand clip 5, wedging it in place, and is cut off by drawing it against the adjacent edge [8. In this position the tape {I1 is drawn tightly against the outer face of each element In, due to the longitudinal tension on the tape, the curvature of the strip I I and the spring pressure of said strip.

The insulating liquid, which may be lacquer, varnish, paint or the like, can then be readily applied to the exposed lateral segments of the elements ID, as by brushing or spraying with one hand while the jig is held in the other. The strip of the masking tape under production conditions while assuring the accurate centering of the tape across the exposed semi-conducting layers of the rectifier elements Ill. The tape may be of any suitable flexible material, paper of the requisite strength having been found especially suitable and inexpensive, since it may be obtained in large rolls and discarded after use.

While the preferred embodiment of the invention has been described, this has been done by way of illustration and not limitation, since various modifications may be employed without departing from the scope of the invention.

scribe an arc of acircle with the discs protruding from the convex side thereof, applying a flexible maskingstrip longitudinally across said series of discs along the curved face of said material in position to cover a given area of each of said disc surfaces, and applying tension to said strip to urge it tightly over the faces of said discs while coating material is applied to the exposed portions of said surfaces.

2. In a process'for manufacturing dry disc rectifier elements, the improved method for coating a limited area of each of a series of rectifier discs comprising partially striking up a series of discs from a sheet metal member with the struck up discs in alignment, flexing said member to cause the outer surfaces of said discs to be located along a convex curve, protecting portions of said discs by applying a flexible masking strip along said curve across a portion of the outer surface of each disc, and applying tension to said strip to cause it to engage tightly the surfaces of said discs while a coating material is applied to the exposed portions of said surfaces.

3. In rectifier coating apparatus, a support having a convex curved surface onto which rectifier discs to be coated may be placed in alignment, a flexible masking strip, and means to secure the ends of said strip adjacent the ends of said curved convex surface, said last named means being arranged to hold the strip under tension radially inwardly of said curved surface and across said series of discs to cause it to'engage tightly the surfaces of said discs whereby the portions of the surfaces of the discs covered by said masking strip are protected when coating material is applied to the exposed surfaces of the discs.

4. In apparatus for coating limited areas of rectifier discs partially struck up from a sheet 'metal member comprising means to support said member in a manner to curve the member with the partially struck out discs protruding from a convex curved surface of said member, a flexible masking strip, and means for holding said strip under tension in position lengthwise .across the surfaces of said discs along the convex curved outline thereof to cause the strip to engage tightly V particularly 6. In apparatus according to claim 4 wherein said means for holding said member includes a support having a curved convex surface, means a forming a recess at one end of said curved surface to receive one end portion of said member, means for securing said strip adjacent said one end of said member and means adjacent the other end of the curved surface of said support to hold said strip under tension, whereby said strip when drawn under tension over said member causes said member to conform to the curved surface of said support.

7. A jig for holding a flexible masking strip against aligned rectifier discs carried by a flexible mounting during coating, which comprises a support for the mounting arranged to hold the mounting in convex position, and retaining devices for the end portions of the strip carried by the support arranged to retain the strip in position during coating, each of said retaining devices comprising a clip including a clamping part and a bending edge located diagonally across the path of said strip.

8. A support for a plurality of rectifier discs to be coated after aligning a masking strip against said discs which comprises a convex surface on the support, the said rectifier discs being aligned on said convex surface, a flexible masking strip adapted to cover a part of each of the said discs and a clip adjacent each end of said convex surface to hold the strip in masking position against said discs, each clip including a clamping part and a bending edge located diagonally across the path of the strip.

, WILLIAM E. RIECKEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Wyman July 13, 1943 

